Split system ice-maker with remote condensing unit

ABSTRACT

A split system ice-maker having a main unit, which houses the ice-making evaporators, and a remote unit, which houses an accumulator, a compressor and a condenser. At least two refrigeration lines are provided which connect the main unit to the remote unit. A four-way valve is located in the remote unit which directs the flow of refrigerant from the compressor to the condenser and then to the evaporator, during an ice-making mode, and additionally directs the flow of refrigerant directly to the evaporators during a harvest mode. The reversed flow in harvest mode briefly defrosts the evaporators, containing the ice-making grid, facilitating harvesting of the ice.

BACKGROUND OF THE INVENTION

The invention relates to the art of ice-making machines, and moreparticularly, to an improved ice-making machine wherein the heat andnoise producing components are installed at a remote location, apartfrom the evaporator.

Typically, large ice-makers that are found in hotels, restaurants andcommercial establishments take up significant floor space, and arenoisy. They also have the further disadvantageous effect of producing atremendous amount of heat at the site where they are located. Theirsize, noise and heat production typically limits where they can belocated. Moreover, where conventional ice-makers require servicing, thetechnicians would typically be in a high traffic area in order to accessthe ice-maker. In order to overcome these disadvantages, the presentinvention provides an ice-making machine wherein the compressor andcondenser are separated from the ice-making evaporator to eliminate muchof the heat and noise associated with conventional ice-making machines.

PRIOR ART

At least one attempt has been made to provide a remote ice-makingsystem. This is described in U.S. Pat. No. 4,276,751, to Saltzman et al,which discloses a typical hot gas system which is well-known in the art.During ice-making, chilled refrigerant passes through a remote line tothe evaporator and then returns on a return line. During harvesting, hotgas is pumped to the evaporator through a third remote line and returnson the same, common return line. The patent to Saltzman et al hasseveral drawbacks in that the thermodynamics of such a system do notpermit the compressor to be located any great distance from theevaporator. Additionally, to the extent that it can be placed remotely,three lines are required between the two units, and the refrigerant,condensed in the evaporator during harvest is returned directly to thecompressor rather than being evaporated in a second heat exchanger, asin the present invention.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to eliminate theaforementioned drawbacks of the prior art and to provide a split systemice-maker, wherein the components, compressor and condenser are locatedseparately from the ice-making unit to isolate the heat and noiseproducing components from the ice making section.

It is a further object of the present invention to provide an ice-makingevaporator which is sufficiently small that it can be placed in manylocations which are not currently feasible with state of the artice-makers.

It is a further object of the present invention to provide asplit-system ice maker wherein the remote condensing unit is capable ofoperating at greatly reduced ambient temperatures and still be capableof generating sufficient heat to adequately harvest ice.

It is still a further object of the invention to provide an ice-makingsystem that is simple in design, easy to maintain, and reliable inoperation.

BRIEF SUMMARY OF THE INVENTION

These and other related objects are achieved, according to theinvention, by a split system ice-maker which operates like a heat pumpand utilizes a four-way valve. The evaporator ice-maker and the receiveris designed as one unit to be placed wherever ice-making capacity isdesired. It is believed that currently existing ice-making evaporatorunits can be used for this purpose. The evaporation unit is connected bytwo remote lines to a second unit, comprising the accumulator,compressor and condenser. Also at the second location is a four-wayvalve which controls the flow of refrigerant during the various cycles.

In the ice-making mode, the four-way valve directs refrigerant from thecompressor through the condenser, and then along a first remote line tothe ice-making evaporators. A second remote line at the output of theevaporators is connected to the input side of the compressor via thefour-way valve. In the ice harvest mode, the compressor output isdirected through the second remote line to the evaporator ice-makers,and then through the first remote line to the condenser. From thecondenser, the four-way valve permits the refrigerant to reach the inputside of the compressor. In the pump down mode, the valve only permitsthe refrigerant to flow from the compressor through the condenser alongthe first remote line to be collected in the receiver, which is locatedin the vicinity of the evaporators.

Thus, the four-way valve permits the condenser and evaporator to switchfunctions between the ice-making and ice harvesting cycles, so that theentire system operates like a heat pump. That is, during the ice-makingmode, the condenser and evaporator operate normally. However, during iceharvesting, the ice-making unit, or evaporator, has to be heated torelease the ice into the ice collection bin. The hot compressor outputis thus fed to the evaporators which absorb heat from the refrigerant,like a condenser. As the refrigerant returns, it passes throughcapillary tubes, which operate as an expansion valve, and chills thecondenser upon contact, like an evaporator.

Since the condenser and evaporator both operate as heat exchangers, andsince they reverse roles, the system is analogous to a heat pump.However, a heat pump has basically a single loop in which all thecomponents are attached. During the reverse cycle, the flow ofrefrigerant is merely reversed in the loop. The heat pump is equippedwith a two-way flow restricter which is disposed between the two heatexchangers, which are generally near each other. Thus, whichever way therefrigerant flows, it encounters a heat exchanger shortly after exitingthe two-way flow restricter.

In the present invention, it is desirable to have one heat exchanger,the ice-making evaporator, indoors where ice-making capacity is desired,and the other heat exchanger, the condenser, located outdoors, where themajority of heat can be dissipated.

The ice-making mode operates for approximately 12 minutes, during whichtime the condenser heats up considerably. Then the ice harvest modeoperates for approximately one to two minutes. During this time, theice-making grid, which is surrounded by ice, is heated by the hot gasoutput of the compressor just enough to melt the bond of the ice to theevaporator so that the ice is removed by gravity. During the ice harvestmode, which lasts only a short time, the indoor heat exchanger, i.e.,the evaporator, does not dissipate heat into the room because theevaporator is only heated enough to allow the removal of the ice. Anadditional benefit is realized at the remotely located outdoor heatexchanger, i.e., the condenser, in that it is momentarily chilled, dueto the introduction of refrigerant undergoing a drastic decrease inpressure. This results in a greater efficiency when the unit cycles backto its ice-making mode.

The compressor and condenser portions of the system are preferablyplaced outdoors behind restaurants and bars, similar to a small centralair-conditioning compressor. In large buildings, such as hotels, theoutdoor unit could be placed on the roof, up to 100 or more feet awayfrom the evaporator.

In another embodiment, several ice-making evaporators could be driven bya single large compressor unit. This eliminates the heat, noise andvibration of the compressor from the occupied areas surrounding theice-making evaporator(s). It is believed that by moving this source ofheat outdoors, one or more tons of additional air conditioning capacitycan be saved.

The invention discloses several features which allow it to operatewithout a two-way flow restriction. It should be pointed out that thereare only two lines between the indoor and outdoor units. The refrigerantflow is reversed in these lines during the two modes of operation. Thus,to an extent, the invention is a single loop, like a heat pump, if theindoor and outdoor units are thought of as individual components.However, a consideration of the refrigerant flow within the indoor andoutdoor units reveals a different situation.

Since the heat exchangers are in different locations, each has its ownflow restricter following a liquid line solenoid. For the ice-makingevaporators, the flow restricter is in the form of an expansion valve.For the condenser, the flow restricter in a preferred embodiment is inthe form of two 0.064" diameter capillary tubes about 30" long, forexample. When a flow restricter is not required, the liquid linesolenoid shuts and refrigerant is routed through other lines which areprovided.

In essence, each liquid line solenoid and its respective flow restricteroperates in one direction during one mode. The four-way valve allows therefrigerant flow to be reversed, so as to accommodate the variouscomponents.

Two lines are connected to the input side of each heat exchanger. One ofthose lines, as discussed above, carries a liquid line solenoid ahead ofa flow restricter. The second line carries a check valve which onlypermits flow away from the heat exchanger. When a heat exchanger isoperating as an evaporator, its liquid line solenoid is open. The checkvalve associated with that evaporator is closed, due to the highpressure upstream from the check valve, i.e., upstream from the flowrestriction. Since the check valve is closed, there is essentially oneline on the input side of the evaporator containing a flow restricter.

When a heat exchanger operates as a condenser, refrigerant flows awayfrom the unit through the check valve. Since the liquid line solenoid isclosed, there is essentially one line containing the check valve leavingthe heat exchanger.

There is also a receiver located in the indoor unit which has severalcheck valves surrounding it. The purpose of this is to cycle refrigerantthrough the receiver continuously, regardless of the mode of operation.This is done to provide proper operation and start up in cold ambientconditions (i.e., -20° F.). During an "idle time" when no ice is beingproduced and the system is in what is called the "pump down" mode ofoperation, the majority of the refrigerant is collected in the receiver.When the receiver is located in the outdoor section, it is subjected tothe outdoor ambient temperature. Consequently, the equalization pressurecorresponds to the ambient temperature. In extremely cold ambients, thisdoes not provide enough pressure differential between the "high" sideand the "low" side to start the system. With the majority of therefrigerant charge in the high side (receiver) from pump down, apressure difference is needed in order to allow the refrigerant to flowto the low side during start up. The compressor will not receive anyrefrigerant to "pump" until this occurs.

By placing the receiver in the indoor unit, it will not be subjected tothe extremely cold ambient temperatures mentioned previously. Thisallows the equalization pressure to be at the corresponding room ambienttemperatures (generally between 65° F. and 80° F.).

To demonstrate how temperature affects the equalization pressure, thefollowing is provided.

    ______________________________________                                                     Equalization Pressure                                            Temperature  (R-22)                                                           ______________________________________                                        -20° F.                                                                              10.1 psig                                                       65° F.                                                                              113.2 psig                                                       80° F.                                                                              143.6 psig                                                       ______________________________________                                    

There is a method of accomplishing these pressures if the receiver islocated in the outdoor section. A strip heater can be placed around thereceiver and operated from a temperature control. This becomes an addedexpense, and requires additional parts which are subject to failure.

Placing the receiver in the indoor unit does not detract from any of thebenefits accomplished by this split system refrigeration scheme. Thereceiver has no moving parts (no noise) and does not reject anyappreciable amount of heat.

A check valve is located at the condenser outlet in the outdoor section.A solenoid valve is provided at the capillary tube inlets. These twodevices keep the refrigerant from flowing back into the condenser duringthe cold ambient pump down mode while the compressor is off.Refrigerants will migrate to the coldest location (in this case, itwould have been the condenser). By eliminating this migration, therefrigerant is contained in the receiver, as desired, as the "high side"pressure remains as described previously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the outdoor unit in ice-making mode;

FIG. 2 is a schematic drawing of the indoor unit during ice-making mode;

FIG. 3 is a schematic drawing of the outdoor unit during harvest mode;

FIG. 4 is a schematic drawing of the indoor unit during harvest mode;

FIG. 5 is a schematic view of the outdoor unit during pump down mode;

FIG. 6 is a schematic drawing of the indoor unit during pump down mode;

FIG. 7 is a table showing the status of the control valves duringvarious modes of operation; and

FIG. 8 is an electrical block diagram of the ice-maker system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now in detail to the drawings, and, in particular, to FIG. 1,there is shown the outdoor unit of a split system ice-maker embodyingthe present invention. The outdoor unit is denoted generally by numeral10. Outdoor unit 10 is connected to the indoor unit, which is generallydenoted by unit 4 (as shown in FIG. 2) through remote lines 12 and 14.It should be noted that remote lines 12 and 14 switch positions as theyextend from FIG. 1 to FIG. 2. (This also occurs when the remote linesextend from FIG. 3 to FIG. 4; and when the remote lines extend from FIG.5 and FIG. 6.)

Outdoor unit 10 and indoor unit 40 form a closed system similar to thatof an air-conditioner, refrigerator, or central air conditioning system.The system is charged to a predetermined level with a refrigerant, forexample, FREON™.

As shown in FIG. 1, in the ice-making mode, a compressor 16 dischargeshigh temperature, high pressure, superheated refrigerant vapor, forexample, FREON™, along a line 18 to a four-way valve 20. Valve 20permits refrigerant to pass through a line 28 to a condenser 30 inice-making mode. Assisted by a fan 32, condenser 30 converts therefrigerant to a sub-cooled liquid refrigerant. Leaving the condenser,along a line 34 through a check valve 36, the refrigerant proceedsthrough line 12 to the indoor unit 40 (as shown in FIG. 2). Refrigerantis prevented from traveling along a line 44, due to a check valve 42,which is located in line 44. Instead, the refrigerant passes through acheck valve 46 to a receiver 48. The refrigerant is prevented fromflowing directly to the evaporators, due to a check valve 50. Uponleaving the receiver, the refrigerant passes through a filter dryer 52and through a liquid line solenoid 54. The refrigerant then encountersan expansion valve 56 and a distributor 58 before reaching one or moreevaporators 60.

The refrigerant flow path is completed when the low temperature, lowpressure vapor returns on line 14 to valve 20, as shown in FIG. 1. Therefrigerant is then routed through accumulator 24 to compressor 16.

Ice-making evaporator 60 is of a conventional design. For example, theice cubes can be formed in one or more vertically or horizontallydisposed freezing surfaces, the back side of which is disposed adjacentto the evaporator. A charge of water is circulated over the freezingsurface or ice making grid. The quantity of water used for each cycle isslightly greater than that needed for ice-making for each harvest cycle.In one embodiment, the charge of water trickles down over a verticallydisposed grid surface from the top, and begins freezing to the walls ofthe grid. With the grid in a vertical orientation, the sediment andminerals in the water settles in a collection tank below the grids,instead of ending up in the ice cubes. Eventually, at the end of theice-making cycle, when the ice cubes are fully formed in each grid, theremaining water is flushed out of the system. With such a configuration,the ice-making mode takes about 12 minutes to complete in the preferredembodiment. In the embodiment shown, a pair of ice-making evaporators 60are mounted against a pair of ice cube grids, as shown in FIG. 2.

After the ice-making cycle has been completed, for example, after 12minutes, the system shifts to its ice harvest mode. FIGS. 3 and 4illustrate the flow of refrigerant during harvest mode. The majordifference between ice-making mode (from FIGS. 1 and 2) and harvest mode(from FIGS. 3 and 4) is that four-way valve 20 routes the hot compressoroutput directly to ice-making evaporators 60, and condenser 30 output isrouted through accumulator 24 to compressor 16. Also, a solenoid valve38 is now open, and solenoid 54 in this embodiment is now closed, butdoes not necessarily have to be closed.

The ice-maker operates very much like a heat pump in the followingsense. The refrigerant flow is reversed in the ice harvest mode fromthat of the ice-making mode so that condenser 30 in FIG. 3 now operatesas an evaporator, and evaporators 60 in FIG. 4 now operate as acondenser. During the harvest mode, refrigerant leaves valve 20 ashigh-temperature, high-pressure, superheated refrigerant vapor andtravels along line 14 to evaporators 60, which are now functioning ascondensers. Due to the low temperature of evaporators 60, therefrigerant is converted to a sub-cooled liquid. Since liquid linesolenoid 54 is closed, at this point, refrigerant flows through a checkvalve 50 and into receiver 48, since check valve 46 prevents any flowinto line 12. After passing through filter-dryer 52, the refrigerantreturns through check valve 42, line 44 to line 12. As can be seen inFIG. 3, since check valve 36 prevents flow, and since solenoid valve 38is open during harvest, refrigerant flows through a pair of capillarytubes 39 to condenser 30, which now operates like an evaporator. In apreferred embodiment, the capillary tubes were 0.064" in diameter andabout 30" long. As an alternative embodiment, solenoid valve 38 andrestricters 39 can be replaced with a thermostatic expansion valve 156similar to valve 56 (see FIG. 5). Upon leaving condenser 30, therefrigerant is converted to a low temperature, low pressure vapor. Theflow is directed along line 28, through valve 20, back to accumulator 24and compressor 16.

There is also a third mode of operation called the "pump down" mode.Pump down is a mode of operation during which no ice is made. Forexample, this occurs when the ice bin is full. Refrigerant flow duringthe pump down mode can be seen in FIGS. 5 and 6. Pump down mode operatesvery similarly to the ice-making mode. This causes the refrigerant togenerally collect in receiver 48 and remote line 12.

As can be seen in FIG. 5, during pump down mode, compressor 16 forceshigh temperature, high pressure super-heated refrigerant through line 18to valve 20. The refrigerant is then routed along line 28 to condenser30. Assisted by fan 32, condenser 30 converts the refrigerant to asub-cooled liquid refrigerant. The refrigerant then passes along line34, through check valve 36, to line 12. As can be seen in FIG. 6,refrigerant passes from line 12 through check valve 46, into receiver48. Up until now, the refrigerant flow is identical to the flow inice-making mode. The longer the pump down mode lasts, the morerefrigerant will collect in receiver 48. In the pump down mode, therefrigerant is never converted to a low temperature, low pressure vaporas during the ice-making mode or harvest modes. This is due to the factthat although the refrigerant passes through condenser 30, it never getsto evaporators 60, but it merely collects in receiver 48 and liquid line12.

Receiver 48 also provides another important function. The three checkvalves around receiver 48, namely check valves 42, 46 and 50, allow therefrigerant to flow through the receiver during both ice-making andharvest modes. This keeps the same volume of refrigerant in circulationduring both modes of operation to provide a balanced system. This alsodirects the refrigerant flow, in one direction, through filter dryer 52in all modes of operation. Moreover, in the pump down mode, refrigerantbuilds up in receiver 48, thus maintaining the "high side" pressure. Asis known from the prior art, a pressure difference is needed in order toallow the refrigerant to flow to the evaporators 60 during start-up. Thecompressor will not start unless it receives refrigerant at its inputend.

The ice-making mode and harvest mode are basically the two phases knownfrom heat pumps. As can be appreciated, the functions of the evaporatorand condenser are reversed during harvest mode. Also, the systemutilizes only two lines, unlike conventional hot gas ice-making systems.Generally, heat pumps have a two way flow restricter. The presentinvention, however, contains two separate flow restricters, namely,expansion valve 56 (as seen in FIG. 2) and capillary tubes 39. Also, theremote unit, as shown in FIGS. 1 and 3, which is ideally placedoutdoors, can be subjected to extremely cold ambient temperatureswithout affecting its function. The refrigerant evaporates into a vaporstate prior to entering the compressor and heat is added to therefrigerant to aid in harvesting. In addition, condenser 30 is chilledduring the ice harvest mode, thus providing for increased efficiencywhen the unit returns to its ice-making mode.

The remote unit, which houses compressor 16 and fan 32, can operate on a220 volt power line as is standard for large air conditioning orrefrigeration units. Single phase or three phase electrical service isideally provided. The ice-making section can operate on 115 volt, singlephase service, which is more readily available in interior areas. Theice making unit and the remote units can be connected via a low voltageor 24-volt AC control circuit. Other than lines 12 and 14, this controlcircuit is the only other connection that is required between the indoorand remote units. The control circuit synchronizes the operations of theindoor unit with the remote unit. For example, after the ice-makingcycle, which is approximately 12 minutes long, the unit would go intoits harvest mode. Thus, valve 20 switches over, solenoid valve 38 opens,and liquid line solenoid 54 can be closed. The operations in the indoorunit are controlled in conjunction with the functions of the remoteunit. The harvest mode continues for one to two minutes, until the icecubes in the grids lose their bond holding them to the grid walls, andfall into the collection bin. The ice-making mode and harvest mode wouldcontinuously alternate until such time as no more ice was required. Thesystem would then go into its pump down mode, or shut down. The pumpdown mode of operation is cycled on and off by the use of a refrigerant(low side) pressure control, that is it will go on at 25 psig and off at5 psig.

Referring to FIG. 7, there is shown a table of the working solenoidvalves for each mode of operation. When the system is in an ice makingmode, four-way valve 20 connects line 18 to line 28 and line 14 toaccumulator 24, and in the harvest mode, connects line 18 to line 14 andconnects line 28 to accumulator 24. Harvest solenoid valve 38 is closedduring the ice making mode, and open during the harvest mode. Liquidline solenoid 54 is open during the ice making mode and closed duringthe harvest mode. In a preferred embodiment, a combination of arefrigerant pressure control, and a preset timer can operate thesevalves to control the two cycles of operation.

FIG. 8 is a block diagram showing one possible method of connecting boththe power lines and the control lines to the active components of themain unit 40 and remote unit 10. A power source 55, such as 110 volts or220 volts, single-phase, can be connected to a control unit 57 whichwill switch the active components into either the ice-making mode, theice harvest mode, or the pump down mode. In the ice-making mode, control57 through control line 59, will operate four-way valve 20, as disclosedin the status diagram of FIG. 7, so as to connect line 18 to line 28 andconnect line 14 to accumulator 24 and compressor 16. Harvest solenoidvalve 38 will be closed, while liquid line solenoid 54 will be open andboth compressor 16 and condenser fan 32 will be operating. Control 57will also close harvest solenoid valve 38 and will open liquid linesolenoid 54 allowing refrigerant to flow into the evaporators.Refrigerant pressure will be sufficient to turn on pressure switch 29,which will supply power 53 to operate both compressor 16 and condenserfan 32. Control unit 57 will also operate water pump 51 to allow waterflow over the evaporator during the ice making process.

In order to change over to the ice harvest mode, a timer, or a pressureswitch 37 connected to the output of evaporator 60, can determine whenthe ice-making process has been completed and cause control 57 to switchto its harvest mode. In the harvest mode, water pump 51 will be shutdown and the residual water in the collection basin below theevaporators will be flushed out. Compressor 16 and condenser fan 32 willcontinue to operate while four-way valve 20 switches to connect line 18to line 14 and to connect line 28 to accumulator 24 and compressor 16.Harvest solenoid valve 38 will then open and liquid line 54 can eitherremain open or be closed, after receiving operating signals from controlline 59.

Control 57 can sense the completion of the ice harvest mode in a numberof conventional ways, such as through the use of a refrigerant pressureswitch at the output of evaporator 60, a timer set, for example, to 90seconds, or other means which senses the dropping of the ice into theice collection bin, as is well known in the prior art. As soon as theice harvest mode has been completed, control 57 will switch the unitback to the ice-making mode. When the ice bin 49 is full of ice, a tripswitch or other device can send a signal to control 57 to switch to thepump-down, so that four-way valve 20 will connect line 18 to line 28 andclose solenoids 38 and 54. Compressor 16 and condenser fan 32 willcontinue to run, storing liquid refrigerant in the receiver, until apressure switch, such as switch 29 in FIG. 5, connected to thecompressor inlet refrigerant line, signals that the proper pressure hasbeen attained. The pressure switch will shut down the compressor andcondensor fan. Between using timers, optical devices, pressure and tripswitches, et cetera, the different modes can be controlled, as is wellknown in the ice-making art.

While only a few embodiments of the present invention has been shown anddescribed, it is to be understood that many changes and modificationsmay be made thereunto without departing from the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:
 1. An improved ice-maker of the type having an ice-making mode and an ice harvesting mode and including a compressor, a condenser, first and second flow restricters, and an ice-making evaporator wherein the improvement comprises:a main unit for housing the ice-making evaporator and the first flow restricter; a remote unit for housing the compressor, the condenser and the second flow restricter coupled to the condenser; two refrigeration lines connecting said main unit to said remote unit, said first line being an evaporator line which during the ice-making mode is an outlet line, and during the harvest mode is an evaporator inlet line and said second line is a liquid line which feeds refrigerant through the first restricter to the evaporator during the ice-making mode, and during the harvest mode, feeds liquid from the evaporator through the second restricter to the condenser; a valve means coupled to said first line, said compressor and said condenser; control means coupled to said valve means wherein, during the ice-making mode, connects the compressor outlet to the condenser, and said evaporator line to the compressor inlet, and during the ice harvest mode, reverses the direction of flow of the refrigerant in said lines and connects the compressor outlet to said evaporator line and the condenser to the compressor inlet so that the condenser serves to evaporate refrigerant and the evaporator serves to condense the refrigerant thereby defrosting the evaporator to facilitate the harvesting of ice; and said valve means additionally includes a harvest solenoid valve coupled to the second flow restricter and a check valve disposed in parallel to said harvest solenoid valve and the second flow restricter, said check valve being closed and said harvest solenoid valve being open during the harvest mode and said check valve being open during the ice-making mode.
 2. The improved ice-maker as recited in claim 1 wherein said valve means comprises a four-way valve having a first part connected to the output of the compressor, and a second part connected to the compressor input; a third part connected to the condenser and a fourth part connected to said evaporator line so that during the ice making mode, refrigerant flows from the first part to the third part and from the fourth part to the second part, and during the ice harvest mode, refrigerant flows from the first part to the fourth part, and from the third part to the second part.
 3. The ice-maker as recited in claim 1, wherein said main unit additionally comprises a receiver coupled between said liquid line and the first flow restricter, and a second check valve in parallel with said receiver and the first flow restricter, wherein during the ice-making mode, the pressure drop through the first flow restricter holds said second check valve closed, and during the ice harvest mode, said second check valve allows unrestricted flow from the evaporator to said liquid line.
 4. The ice-maker as recited in claim 3, additionally including a liquid line solenoid coupled between said receiver and the evaporator, and controlled by said control means for blocking the flow of refrigerant to the evaporator during a pump down mode immediately preceding an off-cycle, and during the off-cycle said control means maintains said harvest solenoid valve shut to prevent migration of liquid refrigerant to the condenser.
 5. The ice-maker as recited in claim 4, additionally comprising an ice bin switch coupled to said control means for switching to the pump down mode when said ice bin switch is activated.
 6. The ice-maker as recited in claim 5, additionally comprising a further pressure switch coupled to the inlet line of the compressor for shutting off the compressor and the condenser at a predetermined pressure level to end the pump down mode and start the off-cycle.
 7. The ice-maker as recited in claim 3 wherein said main unit additionally comprises a third check valve in the liquid line and a fourth check valve in a bypass line from the outlet of the receiver to the liquid line, whereby during harvest mode the refrigerant after it leaves the evaporator is directed into the receiver and from the outlet of the receiver to the liquid line, and during the ice-making mode flows through said third check valve into the receiver and is prevented from bypassing the receiver by said fourth check valve.
 8. The ice-maker as recited in claim 7, wherein the quantity of refrigerant circulating in the system during the harvest mode is approximately the same as the quantity of refrigerant circulating during the ice-making mode.
 9. An improved ice-maker of the type having an ice-making mode and an ice harvesting mode and including a compressor, a condenser, first and second flow restricters, and an ice-making evaporator wherein the improvement comprises:a main unit for housing the ice-making evaporator and the first flow restricter; a remote unit for housing the compressor, the condenser and the second flow restricter coupled to said condenser; at least two refrigeration lines connecting said main unit to said remote unit, one of said lines being an evaporator line which during the ice-making mode is an outlet line, and during the harvest mode is an evaporator inlet line and said second line is a liquid line which feeds refrigerant through the first restricter to the evaporator during the ice-making mode, and during the harvest mode, feeds liquid from the evaporator through the second restricter to the condenser; a valve means coupled to said at least two refrigeration lines, said main unit and said remote unit; and control means coupled to said valve means wherein, during the ice-making mode, connects the compressor outlet to the condenser, and the evaporator line to the compressor inlet, and during the ice harvest mode, reverses the direction of flow of the refrigerant in said lines and connects the compressor outlet to the evaporator line and the condenser to the compressor inlet so that the condenser serves to evaporate refrigerant and the evaporator serves to condense the refrigerant thereby defrosting the evaporator to facilitate the harvesting of ice, said valve means includes (a) a four-way valve having a first part connected to the output of the compressor, and a second part connected to the compressor input; a third part connected to the condenser and a fourth part connected to said evaporator line so that during the ice-making mode, refrigerant flows from the first part to the third part and from the fourth part to the second part, and during the ice harvest mode, refrigerant flows from the first part to the fourth part, and from the third part to the second part; and (b) a harvest solenoid valve coupled to the second flow restricter, and a check valve disposed in parallel to said harvest solenoid valve and the second flow restricter, said check valve being closed and said harvest solenoid valve being open during the harvest mode and said check valve being open and said harvest solenoid valve being closed during the ice-making mode.
 10. An improved ice-maker of the type having an ice-making mode and an ice harvesting mode and including a compressor, a condenser, first and second flow restricters, and an ice-making evaporator wherein the improvement comprises:a main unit for housing the ice-making evaporator and the first flow restricter; a remote unit for housing the compressor, the condenser and the second flow restricter coupled to said condenser; at least two refrigeration lines connecting said main unit to said remote unit, one of said lines being an evaporator line which during the ice-making mode is an outlet line, and during the harvest mode is an evaporator inlet line and said second line is a liquid line which feeds refrigerant through the first restricter to the evaporator during the ice-making mode, and during the harvest mode, feeds liquid from the evaporator through the second restricter to the condenser; a valve means coupled to said at least two refrigeration lines, said main unit and said remote unit; control means coupled to said valve means wherein, during the ice-making mode, connects the compressor outlet to the condenser, and said evaporator line to the compressor inlet, and during the ice harvest mode, reverses the direction of flow of the refrigerant in said lines and connects the compressor outlet to said evaporator line and the condenser to the compressor inlet so that the condenser serves to evaporate refrigerant and the evaporator serves to condense the refrigerant thereby defrosting the evaporator to facilitate the harvesting of ice; said main unit additionally includes a receiver coupled between said liquid line and the first flow restricter, and the evaporators being connected to the first flow restricter; said valve means additionally includes a liquid line solenoid coupled between said receiver and said evaporators for blocking the flow of refrigerant to the evaporators during a pump down mode; and a harvest solenoid valve, wherein during pump down mode, said harvest solenoid valve and said liquid line solenoid valve are closed, and refrigerant flows from said evaporator line to the compressor input and from the output of the compressor to the condenser and to said receiver.
 11. The ice-maker as recited in claim 10, additionally comprising a pressure switch coupled to said evaporator line, said switch being set at a predetermined level to switch said control means from the ice-making mode to the harvest mode.
 12. An improved ice-maker of the type having an ice-making mode and an ice harvesting mode and including a compressor, a condenser, first and second flow restricters, and an ice-making evaporator wherein the improvement comprises:a main unit for housing the ice-making evaporator and the first flow restricter; a remote unit for housing the compressor, the condenser and the second flow restricter coupled to said condenser; at least two refrigeration lines connecting said main unit to said remote unit, one of said lines being an evaporator line which during the ice-making mode is an outlet line, and during the harvest mode is an evaporator inlet line and said second line is a liquid line which feeds refrigerant through the first restricter to the evaporator during the ice-making mode, and during the harvest mode, feeds liquid from the evaporator through the second restricter to the condenser; a valve means coupled to said at least two refrigeration lines, said main unit and said remote unit; control means coupled to said valve means wherein, during the ice-making mode, connects the compressor outlet to the condenser, and said evaporator line to the compressor inlet, and during the ice harvest mode, reverses the direction of flow of the refrigerant in said lines and connects the compressor outlet to the evaporator line and the condenser to the compressor inlet so that the condenser serves to evaporate refrigerant and the evaporator serves to condense the refrigerant thereby defrosting the evaporator to facilitate the harvesting of ice; said main unit additionally includes a receiver coupled between said liquid line and the first flow restricter, and the evaporator being connected to the first flow restricter; said valve means additionally includes a liquid line solenoid coupled between said receiver and said evaporators for blocking the flow of refrigerant to the evaporators during a pump down mode; a pressure switch coupled to the inlet line of the compressor for shutting off the compressor and the condenser at a predetermined pressure level during the pump down mode; and an ice bin switch coupled to said control means for switching from the harvest mode to the pump down mode when said ice bin switch is activated.
 13. A method of making ice using an ice maker with a remote condensing unit, comprising the steps of:providing an ice-making cycle with a first check valve allowing unrestricted flow from a condenser to an ice-making unit, and a first automatic valve allowing flow through a restricter into an evaporator; reversing the flow of refrigerant to provide a harvest cycle with a second check valve allowing unrestricted flow from an evaporator to bypass the first automatic valve and a second automatic valve allowing flow through a restricter into the condenser to bypass the first check valve; trapping the majority of the refrigerant in a relatively warm receiver during an "off" cycle; preventing the refrigerant from migrating to the coldest part of the system in order to provide adequate pressure for start up at the beginning of the next ice-making cycle; and closing the automatic valves in response to control means during the off cycle.
 14. The method as recited in claim 13, wherein the receiver is located in an interior environment.
 15. The method as recited in claim 14, wherein the interior environment is within the main ice-making unit. 